Chromatography is a set of techniques for separating a mixture into its constituents. Well-established separation technologies include HPLC (High Performance Liquid Chromatography), UPLC (Ultra Performance Liquid Chromatography), and SFC (Supercritical Fluid Chromatography). HPLC systems use high pressure, ranging traditionally between 1,000 psi (pounds per square inch) to approximately 6,000 psi, to generate the flow required for liquid chromatography in packed columns. In contrast to HPLC, UPLC systems use columns with smaller particulate matter and higher pressures approaching 20,000 psi to deliver the mobile phase. SFC systems use highly compressible mobile phases, which typically employ carbon dioxide (CO2) as a principle component.
In general, in a liquid chromatography (LC) application, a solvent delivery system takes in and delivers a mixture of liquid solvents to an autosampler (also called an injection system or sample manager), where an injected sample awaits the arrival of this mobile phase. The mobile phase carries the sample through an analytical column (also referred to as a separation column). In the column, the mixture of the sample and mobile phase divides into bands depending upon the interaction of the mixture with the stationary phase in the column. A detector, for example, identifies and quantifies these bands as they exit the column.
Proteomic analyses often utilize a trap column for sample enrichment and cleaning prior to separation of the sample in an analytical column. Often, different packing material chemistries are used for the trap and analytical columns; sample components trapped on the trap column may be serially driven from the trap to the analytical column during a gradient-based mobile phase elution process. The components can be initially focused at the head of the analytical column, because of the different chemistry, until the gradient attains a level that drives the sample components from the chemistry of the analytical column. In addition, some chromatography instruments use a microfluidic substrate. Such substrates can ease the handling of small samples and reduce undesirable effects, such as dispersion.